Randomized Controlled Trials for Post-COVID-19 Conditions: A Systematic Review

Post-coronavirus disease 2019 (COVID-19) syndrome or condition (PCS) is defined as new onset symptoms for at least three months following COVID-19 infection that has persisted for at least two months. Given the global sequelae of COVID-19, there is an urgent need for effective PCS interventions. The aim of this study was to systematically review all interventions for PCS tested in randomized controlled trials. In this International Prospective Register of Systematic Reviews (PROSPERO) registered (CRD42023415835) systematic review, PubMed, Google Scholar, and ClinicalTrials.gov databases were searched between 1st January 2020 and 30th April 2023. Inclusion criteria were (1) randomized controlled trials that tested interventions for (2) PCS as defined above. Studies were independently reviewed, and final decisions regarding extracted data and risk of bias were made by consensus. Trial findings were summarized qualitatively. The review included 23 trials with 1,916 subjects (mean age 44.9, 25.8% males) from 10 countries. The predominant symptom or function targeted by the interventions were general long COVID-19 symptoms (35%), fatigue (30%), breathlessness (17%), olfactory (17%), and brain function (9%). Overall, the majority of trials (74%) were at high risk of bias. A range of interventions were identified, including physical therapies, dietary and regenerative treatments, electrical stimulation, and digital wellness programs with variable effects. While a diverse range of interventions for PCS have been tested, their effectiveness varies, with threats to validity in most studies. Trials focusing on PCS mental health disorders, musculoskeletal complaints, and children are needed. Well-designed RCTs are needed to establish definitive interventions for PCS.


Introduction And Background
The RNA virus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which has ravaged the globe for the past three years, is the source of coronavirus disease 2019 .Due to mutations, there are newly emerging strains of COVID-19 that are highly transmissible without increased disease severity, which allows the virus to be a continuous threat to global health [1].While a high percentage of COVID-19 patients have a full recovery after the initial illness, 20% experience mid-and long-term effects [2].This is referred to as a "long COVID", "post-COVID-19 condition" or "post-acute COVID-19 syndrome (PACS) [3].
PACS can persist for weeks, months, or longer (mid-or long-term), and while it can affect persons who had mild or no symptoms of the illness, it has a high prevalence in persons with a history of severe COVID-19 illness [3].There are general, digestive, respiratory, cardiac, and neurological symptoms that epidemiological studies have found associated with PCS, some of which are fatigue, post-exertional malaise, fever, stomach pain, diarrhea, cough, difficulty breathing, headaches, depression, and joint or muscle pain [3].
Despite the abundance of systematic reviews and clinical trials on acute COVID-19 treatment, an August 2022 review found only two trials specifically addressing interventions for PCAS [2].With the emergence of new interventional studies for PCAS, an updated review is warranted.The aim of this research was to systematically review all interventional studies on PCAS, assess their quality, and synthesize their findings.

Search Strategy and Selection Criteria
This systematic review included randomized controlled trials (RCTs), including cross-over trials, that examined interventions on subjects with post-COVID-19 conditions.This review sought all RCTs that examined interventions on subjects with PCAS in keeping with the WHO definition [4].Participants in eligible trials had continuing or newly developed symptoms at least three months following initial SARS-CoV-2 infection, with persistent symptoms at trial entry without any other explanation.Trials with symptomatic participants at less than 90 days between acute infection and enrolment were excluded.Studies were included if they were published in English from the period 01/01/2020 to 30/04/2023.Noneligible studies were animal studies, cohort studies, case-control studies, in-vitro studies, and trials without a control group.
The literature search was conducted using PubMed, the clinicaltrial.govdatabase, and Google Scholar for grey literature.Creation of title listing for Google Scholar searches was done by Publish or Perish Software which was extracted into spreadsheets to screen titles [5].Authors of studies still recruiting or with unclear recruitment status were contacted for any available preliminary published data.The search strategy used terms related to the post-COVID-19 condition.Full details of the search syntax can be found in Table 1.Using the most recent version of the Cochrane risk-of-bias (RoB2) tool, two authors independently assessed the risk of bias for each study's primary outcome [6].For the deviation from intended interventions RoB2 domain, the effect of assignment to intervention was assessed when intention-to-treat was reported.For studies that did not use an intention-to-treat approach, the effect of adherence to treatment was assessed and presented for this RoB2 domain.For trials that were crossover by design, the supplemental version of RoB2 tailored for assessing such designs was used [7].Disagreements were resolved by consensus.

Database
A qualitative synthesis of all studies was completed.The main results for the primary outcome from each trial were reported comparatively.Risk of bias measures were reported as percentages by domain and qualitatively by trial.The proposal for this review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (No.CRD42023415835) and adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards as shown in

Results
From an initial search yielding 1,340 articles, a total of 23 trials were included in this review which were 18 original published papers, four preprints and one conference abstract.Figure 1 depicts the selection of studies for this review.The excluded trials are detailed in Table 3.
The duration of COVID-19 symptoms was not reported and the author was unable to verify [17].
Examined prevention of post-COVID19 condition in acutely infected participants [20].

TABLE 3: Excluded studies
Collectively, the included trials allocated 1,916 subjects from 10 countries (Brazil, China, Denmark, France, Israel, Italy, Poland, Spain, United Kingdom, and the USA).The weighted mean age of all subjects was 44.9 years with 25.8% males.There was one pediatric study whose participants had an average age of 10.8 years, and 42% were males.The majority of studies (83%) recruited participants from outpatient clinics or the community.Of the 17 studies that reported a mean time from initial COVID-19 infection to enrolment or receipt of intervention, the overall mean was 256.6 days.For the remaining six studies, the range of time between acute infection and enrolment spanned 90-360 days.The predominant symptom or function targeted by the interventions in the trials were general long-COVID-19 symptoms (35%), fatigue (30%), breathlessness (17%), olfactory dysfunction (17%), and brain function (9%).With regards to the diagnosis of COVID-19, 10 (43%) of the trials did not explicitly state the use of polymerase chain reaction (PCR), however, all these studies stated in their inclusion criteria that participants must have had prior COVID-19 infection diagnosed.
Sample sizes were calculated in the majority (78%) of studies.Of the 18 studies with calculated sample sizes, the trial was adequately powered by allocated subjects in 15 (83%).Blinding status was double, single, and unblinded in 10 (44%), six (26%), and 7 (30%) of the trials, respectively.Published protocols were available for three (13%) of the studies, with the majority of studies (83%) registered on clinicaltrials.gov.Study characteristics of the included trials are shown in Table 4 [

TABLE 4: Characteristics of included trials
The risk of bias of the 23 included studies are shown by domain in Figure 2. Overall, the majority of trials (74%) were at high risk of bias, with some concerns in three (13%) and low risk in three (13%) trials.The second RoB domain (deviation from intended interventions) was at greatest risk for high concerns.Almost a third (7/23) of the studies carried out an intention-to-treat (ITT) analysis, while the remainder did a per-protocol analysis.None of the studies that did a per-protocol analysis reported any evidence of appropriate analyses used to estimate the effect of adhering to the intervention.The proportion of ITT studies that had a high risk of bias on domain 2 was 0% vs. 75% of the per-protocol analysis studies (P=0.001).The proportion of ITT studies that had a high overall risk of bias was 43% vs. 88% of the perprotocol analysis studies (P=0.045)Blinding status (double-blind vs non-double-blind) was independent of overall bias risk (P=0.341).Figure 3 summarizes the judgment for each RoB domain and the overall risk for all studies.
FIGURE 3: Risk of bias assessments for individual studies  The agreement on all five RoB domains after the preliminary independent review was 86%.A range of interventions were employed across the 23 trials, which encompassed physical therapies, dietary supplements, electrical stimulation, and digital wellness programs.The specifics of the treatments tested and their reported effects on the trials' primary outcomes are summarized below by PCAS condition.
Seven studies focused on PCAS patients mainly suffering from fatigue.Interventions involved L-arginine and vitamin C supplementation [22,39], high-definition transcranial direct current stimulation [34,38], home-based respiratory muscle training [25], water-based and land-based exercise training programs [33] and essential oil inhalation [28].Significant improvement was noted in patients undergoing L-arginine and Vitamin C supplementation [39], home-based respiratory muscle training [25], and essential oil inhalation [28].There were mixed results in those who received high-definition transcranial direct current stimulation [34,38].The other interventions did not show significant comparative benefits in fatigue scores.
Two trials separately investigated the effect of co-ultramicronized palmitoylethanolamide/luteolin [41] and hyperbaric oxygen therapy [23] [25], and water and land-based exercise programs [33].Significant results were seen for the online breathing program and inspiratory muscle training, improving mental health [36] and reducing breathlessness [32], respectively.The other two trials did not demonstrate significant improvements [25,33].
Four studies examined interventions for PCAS patients suffering from olfactory dysfunction.Three of the trials, which investigated oral ultramicronized palmitoylethanolamide and luteolin supplements [26], a combination of short-course oral vitamin A with aerosolization diffuser olfactory training [24], and plateletrich plasma injections [42] found significant improvements.The study that examined bimodal visualolfactory training with patient-preferred scents did not show any difference between the active intervention arms [31].

Discussion
From an initial search yielding 1,340 articles, a total of 23 randomized controlled trials were included in this systematic review.The various trial settings were geographically diverse, spanning the American, Asian and European continents with mostly outpatient participants.The gender predominance of women seen in the studies of this review is in keeping with the literature.In one cohort, long COVID-19 reportedly occurred more than three times the odds in women compared to men [44].The studies found in this review enrolled predominantly adults with only one pediatric trial.The prevalence of PCAS in children has been estimated to be around 23%, almost half that of adults [45].This may explain the paucity of PCAS trials in children and adolescents.Meta-analysis and Grading of Recommendations Assessment, Development and Evaluation (GRADE) assessments could not be done as part of this review as there were no studies assessing the same population, intervention, and outcomes.This, coupled with the high risk of bias in most trials, limits recommendations that can be made in favor of any of the interventions examined in this review.

Post-Acute Sequelae of Non-COVID-19 Viral Illnesses
Long haulers following viral illnesses are not specific to COVID-19.Symptoms similar to PCAS have been described following past influenza pandemics since the late 19th century [46,47].Additionally, the similarities between PCAS and myalgic encephalomyelitis/chronic fatigue syndrome have been well described [48].Do effective interventions exist, given our history with these long-term post-viral sequelae?A 2015 systematic overview of interventions for chronic fatigue syndrome found moderate certainty evidence (GRADE) for graded exercise, moclobemide, and hydrocortisone and low certainty evidence (GRADE) for cognitive behavioral therapy and selected antidepressants [49].Similarly, for post-viral olfactory dysfunction, olfactory training has been the intervention with the most support during pre-COVID-19 times [50].These prior studies can offer future direction for potential PCAS interventions

Next Steps
There exists room for better designed trials even for the PCAS conditions explored in this review.In this review there was a significant association with studies that did only a per protocol analysis and high risk of bias.Although an ITT analysis is not always feasible, none of the per-protocol studies reported appropriate analyses to estimate the effect of adhering to the intervention as suggested by RoB2.Researchers should consider all RoB2 domains and signaling questions when designing trials.
A meta-analysis studying post-COVID-19 populations found that over 20% experience persistent fatigue and breathlessness, while at least 10% suffer from anxiety, depression, insomnia, post-traumatic stress disorder, joint pains, and myalgia [51].Interestingly, none of the eligible trials in our systematic review focused on populations with these mental disorders and musculoskeletal conditions.A review of registered trials looking at interventions for key mental conditions in PCAS revealed plans for 42 trials that were yet to be completed at the time of this review [52].As time progresses, updates to this review will reveal the true extent of effective interventions for the wide spectrum of PCAS.There is also a need for PCAS trials in the pediatric age group, seeing that they are not spared from the long-term effects of COVID-19 and were underrepresented in this review.

Strengths and limitations
This systematic review had some key strengths.The comprehensiveness of the review was ensured by welldefined eligibility criteria.The inclusion criteria of trials that enrolled or randomized participants with new and ongoing symptoms at least 90 days post-acute COVID-19 infection optimized the inclusion of eligible long COVID-19 trials.The search strategy spanned multiple sources and included unpublished trials.The use of paired independent reviewers and the application of the Cochrane risk-of-bias [RoB2] tool for independent risk-of-bias assessment lent rigor to the analysis.Lastly, in summarizing all PCAS trials, this review revealed significant research gaps which can guide further research.
There are a few limitations of this review.Firstly, it was limited to English literature and may have missed articles published in other languages.Secondly, it is possible that eligible papers could have been missed, especially if they were not described as trials in their title.Thirdly, the grey literature was sourced through Google Scholar, though its coverage may not be exhaustive and there is a possibility that unpublished trial reports may have been overlooked.Lastly, PCR confirmation of COVID-19 was not explicitly stated in all studies.However, these studies' inclusion criteria required participants to not only have an initial diagnosis of COVID-19 infection but also to exhibit the development of new symptoms post-diagnosis.

Conclusions
This systematic review found most of the trials on interventions for treating post-COVID-19 syndrome were at high bias risk.Although previous non-COVID-19 post-viral and existing post-COVID-19 syndrome trials provide some treatment leads, further robust trials and novel treatments are needed.Interventional study research gaps also exist for post-COVID-19 mental disorders, musculoskeletal issues, and pediatric patients.

FIGURE 1 :
FIGURE 1: PRISMA diagram depicting the selection of eligible studies PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses

(
Serum concentrations of l-arginine, citrulline, ornithine and other amino acids with ratios.Serum l-arginine concentrations and lolfactory function by the butanol threshold test (BTT) between baseline and end-of-treatment.At end-of-treatment, mean butanol threshold test scores were significantly higher for the combination group when compared to control (p<0.001) and standard care (p=0.009)groups.quality of life and exercise tolerance At post-intervention, there was a statistically significant and large (d>0.90)improvement in quality of life, but not in exercise tolerance, in the inspiratory and expiratory muscle group compared with the sham equivalent.capsules of Coenzyme Q10 in a dose of 500 mg/day or placebo for 6 n=60, placebo oral capsules for 6 weeks, with crossover Change in the number and/or severity of Post COVID19 Condition related The difference between Coenzyme Q10 and placebo was not significant with respect to either the change in health index (p = 0.45) 2024 Motilal et al.Cureus 16(8): e67603.DOI 10.7759/cureus.theessential oil blend for 2 weeks had significantly lower fatigue scores after controlling for baseline scores, employment status, BMI, olfactory function, and time since diagnosis, with a large effect size ( p = .020)the change pre-post intervention favored the exercise group in cardiovascular and strength markers (p < 0.05).In addition, exercise intervention resulted in a significantly better quality of life, less fatigue, less depression, and improved functional status, as well as in superior cardiovascular fitness and muscle strength compared to controls (p < 0.05). in VO2 max, handgrip strength and bench press one repetition among all 4 groups.(P>0.05).Both concurrent training intervention groups significantly different to control group for bench press and half squat mean velocities, and half-squat one-repetition maximum care Health-related quality of life There was no difference between groups in total score post-intervention.Muscle training elicited clinically meaningful improvements in the subdomains of breathlessness and chest symptoms (P<0.05)Impact Scale score was used as the primary endpoint.There were no statistically significant intergroup differences in the percentage of patients showing a clinically significant change in fatigue scores at the end of treatment (P = 0.440) Palau et al., muscle training at home twice daily using a threshold inspiratory muscle trainer for 12 weeks n=13, usual care Average change from baseline in mean peak VO2 The mean of peakVO2 was 22.2 mL/kg/min (95% CI 21.3 to 23.2) compared to control, care Change in health-related quality of life using RAND 36-item short form survey instrument mental health composite and physical health composite scores Mental health composite score change was statistically significant compared to placebo P =0.047.Physical health composite score change was not statistically significant compared to control P=0.54.The change from baseline to day 28 in distance walked on a 6min walk test l-arginine plus vitamin C significantly increased the distance walked on the 6 min walk test (p = 0.001) significant group-by-time interaction in the global cognitive score postoxygen therapy compared to the control group (p= 0.038).Both attention and executive function domains had significant group-by-time interactions (p= 0.

FIGURE 2 :
FIGURE 2: Distribution of risk of bias by study domain

TABLE 1 : Search strategy
Study Quality and Data AnalysisPaired reviewers (JL, AW; AS, TR; RR, SGL; and MA, AR.) independently screened articles by title, abstract, and then full text to determine eligibility for final inclusion.Any disagreements between the authors were discussed, and a final decision was made by SM after consensus meetings with reviewers.SM extracted data from the final selection of articles into a spreadsheet, which was checked by a second reviewer JL.Missing data was requested from the study authors firstly by SM and then JL if no initial response.No assumptions were made where data was missing.
INTRODUCTION Rationale 3 Describe the rationale for the review in the context of existing knowledge.Background Objectives 4 Provide an explicit statement of the objective(s) or question(s) the review addresses.

RESULTS Section and Topic Item # Checklist item Section where the item is reported 16a
Describe the results of the search and selection process, from the number of records identified in the search to the number of studies included in the review, ideally using a flow diagram.Present results of all statistical syntheses conducted.If meta-analysis was done, present for each the summary estimate and its precision (e.g.confidence/credible interval) and measures of statistical heterogeneity.If comparing groups, describe the direction of the effect.
Results 16bCite studies that might appear to meet the inclusion criteria, but which were excluded, and explain why they were excluded.ResultsStudy characteristics 17Cite each included study and present its characteristics.evidence22Present assessments of certainty (or confidence) in the body of evidence for each outcome assessed.N/A DISCUSSION Discussion 23a Provide a general interpretation of the results in the context of other evidence.Discussion 23b Discuss any limitations of the evidence included in the review.Discussion 23c Discuss any limitations of the review processes used.Discussion 23d Discuss implications of the results for practice, policy, and future research.Discussion OTHER INFORMATION Registration and protocol 24a Provide registration information for the review, including register name and registration number, or state that the review was not registered.Methods 24b Indicate where the review protocol can be accessed, or state that a protocol was not prepared.Methods 24c Describe and explain any amendments to information provided at registration or in the protocol.N/A Support 25 Describe sources of financial or non-financial support for the review and the role of the funders or sponsors in the review.27Reportwhich of the following are publicly available and where they can be found: template data collection forms; data extracted from included studies; data used for all analyses; analytic code; any other materials used in the review.

TABLE 2 : PRISMA Checklist
N/A: Not applicable; PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses on brain function.Both interventions led to significant enhancements in brain function parameters.Four studies investigated interventions for breathlessness PACS subjects, including an online breathing and wellbeing program [36], unsupervised inspiratory muscle training [32], a home-based respiratory muscle training program